why won't my GFCI plug reset-button reset? It is flashing red and I am unable to get the reset button to pop back.
If you know the manufacturer of the GFCI you could probably look up to see what a flashing red light means, but I'm guessing it indicates a miswired GFCI or some other kind of internal failure.
If you just installed the GFCI, double-check that the wiring has been done properly (i.e. you did not swap the LINE and LOAD sides, swap hot & neutral, etc).
If it is an old GFCI, maybe it is just time to replace it. They can fail over time, especially older models were more prone to failure.
Is the situation that cause the GFCI to trip still existing? Did the electrical panel circuit breaker also trip? If so, was it switched back "on"? Are you pressing the reset button in far enough?